This invention relates to a line spacing device for a typewriter, and more particularly to an automatic line spacing device which includes a ratchet wheel mounted for integral rotation with a cylinder platen, and a feed pawl mounted for engagement with the ratchet wheel for incrementally feeding a paper sheet carried on the platen.
Automatic line spacing devices for electrically operated typewriters are already known which include a ratchet wheel mounted for integral rotation with a cylinder platen and a feed pawl mounted for engagement with the ratchet wheel for incrementally feeding a paper sheet carried on the platen. Conventionally, most of such typewriters include a constantly rotating power shaft coupled to an electric motor, which is in most cases an AC motor, and the power shaft is operatively coupled to the feed pawl of such line spacing devices by way of a suitable motion converting means for converting the rotational motion of the power shaft into a linear or circular or any other suitable reciprocating motion of the feed pawl. The motion converting means may conventionally include a cycle clutch mechanism or an eccentric cam mechanism and an associated link mechanism.
Recently, "daisy wheel" typewriters have been so popular that less and less effort is made to develop power driven typewriters of any other conventional type, such as a "type bar" type. The daisy wheel typewriters normally have no such constantly rotating power shaft and include a daisy wheel type wheel which is conventionally coupled to either a stepping motor or a servomotor for rotating the type wheel to bring a selected character type to a print position for printing. Normally, in these typewriters, a separate slectric motor is provided for a ribbon mechanism and for a line spacing function and/or an escapement or spacing function.
Conventionally, a stepping motor is used for the line spacing function which is constantly coupled to the platen by way of a transmission including several toothed gear elements such that a fraction or step of rotation of the motor in either direction will cause a smaller fraction of rotation of the platen in a corresponding direction. Employment of the stepping motor is advantageous in that it eliminates the use of complicated motion converting structure typically including detent means for the platen and allows employment simple reduction gear mechanism. However, employment of the stepping motor will result in an undesired high production cost for a line spacing device since, in addition to a relatively high cost of the stepping motor itself, all of the components of the associated reduction gear mechanism must be very accurately made, and the complexity of the circuit for controlling the stepping motor cannot be eliminated.